The goal of this proposal is to develop a novel therapeutic strategy for the treatment of multiple myeloma employing checkpoint abrogators such as UCN-01 in combination with inhibitors of the MEK1/2/MAP kinase pathway. It is based upon the recent discovery that exposure of multiple myeloma and other malignant hematopoietic cells to UCN-01 increases activity of p34cdc2(cdk1), an event associated with MAP kinase activation. Furthermore, interruption of the latter process (e.g., by pharmacologic MEK inhibitors such as U0126 or PD184352) results in a dramatic increase in mitochondrial injury, caspase activation, and apoptosis. Significantly, UCN-01/MEK inhibitor-mediated lethality toward myeloma cells is undiminished by conventional or cell adhesion-related drug resistance mechanisms, or by exogenous survival-related cytokines such as IL-6 and IGF-1. Finally, consistent with evidence that neoplastic cells are selectively impaired in checkpoint control, primary CD138+ bone marrow-derived human myeloma cells appear to be significantly more sensitive than their normal counterparts to this novel strategy. The specific aims of this proposal are a) to elucidate the mechanism(s) by which UCN-01 and MEK inhibitors interact synergistically in myeloma cells, focusing on the functional significance of perturbations in signaling/cell cycle regulatory pathways (e.g., p34cdc2, Raf/MEK/MAP kinase, NFkB, p27KIP1, and cyclin D1; b) to test the hypothesis that the anti-myeloma activity of the UCN-01/MEK inhibitor regimen can be further enhanced by coadministration of proteasome inhibitors, possibly by sparing the cdc25C phosphatase; c) to test the hypothesis that the clinically relevant geldanamycin analog 17-AAG interacts synergistically with UCN-01 in myeloma cells by mimicking the ability of MEK inhibitors to disrupt the cytoprotective MAP kinase cascade; and d) to establish whether these regimens exert selective toxicity toward primary human myeloma cells while sparing their normal hematopoietic counterparts. It is anticipated that information derived from this proposal will serve as a foundation for initiating Phase I trials combining checkpoint abrogators such as UCN-01 with pharmacologic MEK inhibitors in the treatment of multiple myeloma and possibly other hematologic malignancies. Such studies may also provide a paradigm for the development of a novel therapeutic strategy in which inhibitors of cell cycle regulatory and survival signal transduction pathways are rationally combined in the treatment of cancer.